JP7258000B2 - Manufacturing method of resin porous body - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a resin porous body.

Porous resin bodies using water-insoluble polymers can exhibit various properties such as lightness, cushioning properties, heat insulation properties, sound absorption properties, separation properties, and adsorption properties. Therefore, porous resin bodies using water-insoluble polymers are used in a wide variety of applications such as packing materials, building materials, sound absorbing materials, cleaning products, cosmetic products, separation membranes, adsorbents, purification carriers, catalyst carriers, and culture carriers. Used for crossing purposes.

From the standpoint of production cost and the like, it is desired that the method for producing a resin porous body using a water-insoluble polymer be simple. Therefore, as a method for easily producing a porous body of polyvinylidene fluoride, which is a water-insoluble polymer, Patent Document 1 discloses that polyvinylidene fluoride is heated in a mixed solvent of a good solvent and a poor solvent. dissolving to prepare a solution, cooling the solution to obtain a molded article, immersing the molded article in another solvent to replace the mixed solvent with another solvent, and removing the other solvent A method for producing a porous body of polyvinylidene fluoride is disclosed, which includes drying and removing.

JP 2011-236292 A

However, the manufacturing method of the above-mentioned prior art requires many steps such as preparation of a water-insoluble polymer solution, deposition of a molded body, replacement of the solvent, and drying. Further, the present inventors have found that a skin layer (skin layer) having no pores is likely to be formed on the surface of the porous resin body in the production of the porous resin body. When the porous resin body has a skin layer, there is a disadvantage that fluid cannot permeate through the porous resin body, which limits the applications of the porous resin body.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method capable of producing a porous resin body in which the formation of a skin layer is suppressed in a small number of steps using a water-insoluble polymer.

The method for producing a porous resin material disclosed herein comprises adding a solution in which the water-insoluble polymer is dissolved in a mixed solvent containing a good solvent for the water-insoluble polymer and a poor solvent for the water-insoluble polymer. and drying the solution to remove the mixed solvent. The boiling point of the poor solvent is higher than the boiling point of the good solvent. Drying of the solution is carried out using superheated steam. According to such a configuration, it is possible to provide a method for producing a porous resin body in which the formation of a skin layer is suppressed, using a water-insoluble polymer, in a small number of steps.

In a preferred embodiment of the production method disclosed herein, after the step of preparing the solution and before the step of drying the solution, the prepared solution of the water-insoluble polymer is placed on the surface of the base material. It further includes a step of coating the with a thin film. According to such a configuration, it is possible to provide a method for producing a porous resin membrane in which the formation of a skin layer is suppressed, using a water-insoluble polymer, in a small number of steps. Here, when the substrate is an electrode of a secondary battery, an electrode-integrated separator of the secondary battery can be produced.

From the viewpoint of the use of the resulting porous resin material and the usefulness of the method for producing the porous resin material, in a preferred embodiment of the production method disclosed herein, the water-insoluble polymer is an ethylene-vinyl alcohol copolymer. or a vinylidene fluoride-hexafluoropropylene copolymer.

It is a graph for comparing the enthalpy of superheated steam and the enthalpy of hot air. It is explanatory drawing of an example of the implementation method of the drying process in the manufacturing method which concerns on this invention. 4 is a SEM photograph of the surface of the porous membrane obtained in Comparative Example 1. FIG. 2 is a SEM photograph of the surface of the porous membrane obtained in Example 1. FIG. 4 is a SEM photograph of the surface of the porous membrane obtained in Example 3. FIG.

In the method for producing a porous resin material of the present invention, a solution is prepared by dissolving the water-insoluble polymer in a mixed solvent containing a good solvent for the water-insoluble polymer and a poor solvent for the water-insoluble polymer. It includes a step (hereinafter also referred to as “solution preparation step”) and a step of drying the solution to remove the mixed solvent (hereinafter also referred to as “drying step”). Here, the boiling point of the poor solvent is higher than that of the good solvent. Drying of the solution is performed using superheated steam.

First, the solution preparation process will be described. In the present invention, "a good solvent for water-insoluble polymers" means a solvent that exhibits a solubility of 1% by mass or more at 25°C for water-insoluble polymers. The good solvent preferably exhibits a solubility of 2.5% by mass or more, more preferably 5% by mass or more, and 7.5% by mass at 25° C. for the water-insoluble polymer. More preferably, it exhibits a solubility of 10% by mass or more, and most preferably exhibits a solubility of 10% by mass or more. The type of good solvent used in the present invention is appropriately selected according to the type of water-insoluble polymer. The good solvent may be a single solvent or a mixed solvent in which two or more solvents are mixed.

In the present invention, the term “poor solvent for water-insoluble polymer” refers to a solvent that exhibits a solubility of less than 1% by mass at 25° C. for the water-insoluble polymer. The poor solvent preferably exhibits a solubility of 0.5% by mass or less, more preferably 0.2% by mass or less, at 25 ° C. with respect to the water-insoluble polymer. More preferably, it exhibits a solubility of 0.05% by mass or less, and most preferably exhibits a solubility of 0.05% by mass or less. The type of poor solvent used in the present invention is appropriately selected according to the type of water-insoluble polymer. The poor solvent may be a single solvent or a mixed solvent in which two or more solvents are mixed.

The Hansen Solubility Parameter (HSP) can be used to determine whether a particular solvent is a good solvent or a poor solvent for a particular polymer compound. For example, the HSP dispersion term, polarization term, and hydrogen bond term of the polymer compound are δ _D1 , δ _P1 , and δ _H1 , and the HSP dispersion term, polarization term, and hydrogen bond term of the solvent are δ _{D2 ,} respectively. , δ _P2 , δ _H2 , the smaller the value of the HSP distance Ra (MPa ^1/2 ) between the polymer compound and the solvent represented by the following formula, the higher the solubility of the polymer compound tends to be. be.
Ra ² = 4(δ _D1 - δ _D2 ) ² + (δ _P1 - δ _P2 ) ² + (δ _H1 - δ _H2 ) ²

Further, when the interaction radius of the above-mentioned specific polymer compound is R ₀ , it is soluble when the ratio of Ra/R ₀ is less than 1, partially soluble when the ratio of Ra/R ₀ is 1, and Ra/R ₀ ratios greater than 1 are predicted to be insoluble.

Alternatively, by conducting a test in which a specific polymer compound and a specific solvent are mixed in a sample bottle, etc., it is easy to determine whether the solvent is a good solvent or a poor solvent for the polymer compound. can be discriminated.

The good solvent and the poor solvent are mixed and used as a uniform solvent. Therefore, the good solvent and the poor solvent are compatible with each other. In the present invention, the boiling point of the poor solvent used is higher than the boiling point of the good solvent used. The boiling point of the poor solvent is preferably 10° C. or higher, more preferably 90° C. or higher, than the boiling point of the good solvent, since the porosity is relatively high and a homogeneous porous body can be easily obtained. The boiling point of the poor solvent is preferably less than 300°C from the viewpoint of drying speed.

In the present invention, the term "water-insoluble polymer" refers to a polymer having a solubility in water at 25°C of less than 1% by mass. The solubility of the water-insoluble polymer in water at 25° C. is preferably 0.5% by mass or less, more preferably 0.2% by mass or less, and even more preferably 0.1% by mass or less.

The "water-insoluble polymer" used in the solution preparation step is the same polymer as the water-insoluble polymer that constitutes the porous compact. As the water-insoluble polymer, one in which a good solvent and a poor solvent exist is used. The type of water-insoluble polymer to be used is not particularly limited as long as a good solvent and a poor solvent are present. Examples of water-insoluble polymers include olefin resins such as polyethylene and polypropylene; fluorine resins such as polyvinyl fluoride, polyvinylidene fluoride, and vinylidene fluoride-hexafluoropropylene copolymer; polymethyl (meth)acrylate and polyethyl (Meth) acrylic resins such as (meth) acrylate; styrene resins such as polystyrene, styrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene copolymer; water-insoluble such as ethyl cellulose, cellulose acetate, cellulose propionate cellulose derivatives; vinyl chloride resins such as polyvinyl chloride and ethylene-vinyl chloride copolymers; ethylene-vinyl alcohol copolymers; A water-insoluble polymer obtained by modifying a water-soluble polymer can also be used. Among them, from the viewpoint of the usefulness of the water-insoluble polymer porous body and the usefulness of the method for producing the same, the water-insoluble polymer is an aliphatic polymer compound (that is, a polymer compound having no aromatic ring). is preferably Since the porosity is relatively high and it is easy to obtain a homogeneous porous body, the water-insoluble polymer is an addition polymerization type polymer compound (that is, a monomer having an ethylenically unsaturated double bond, the ethylene It is preferably a polymer compound produced by polymerization of a polyunsaturated double bond; eg, a vinyl-based polymer, a vinylidene-based polymer). From the viewpoint of the usefulness of the porous material having a three-dimensional network-like porous structure and the usefulness of the method for producing the same, the water-insoluble polymer is an ethylene-vinyl alcohol copolymer or vinylidene fluoride-hexafluoro A propylene copolymer is preferred.

The average degree of polymerization of the water-insoluble polymer is not particularly limited, but is preferably 70 or more and 500,000 or less, more preferably 100 or more and 200,000 or less. Incidentally, the average degree of polymerization of the water-insoluble polymer can be determined by a known method (eg, NMR measurement, etc.).

Preferred good solvents and suitable poor solvents will be specifically described below using specific water-insoluble polymers as examples. The production method of the present invention can be advantageously carried out by using the good solvent and poor solvent described below for the following water-insoluble polymers. The good solvents listed below can be used singly or in combination of two or more. The poor solvents listed below can be used singly or in combination of two or more.

1. Water-Insoluble Polymer is Ethylene-Vinyl Alcohol Copolymer Ethylene-vinyl alcohol copolymer (EVOH) is a copolymer containing ethylene units and vinyl alcohol units as monomer units. The content of ethylene units in EVOH is not particularly limited, but is preferably 10 mol% or more, more preferably 15 mol% or more, still more preferably 20 mol% or more, and particularly preferably 25 mol%. % or more. The content of ethylene units in EVOH is preferably 60 mol % or less, more preferably 50 mol % or less, still more preferably 45 mol % or less. The degree of saponification of EVOH is not particularly limited, but is preferably 80 mol% or more, more preferably 90 mol% or more, and still more preferably 95 mol% or more. The upper limit of the degree of saponification is determined by technical limits regarding saponification, and is, for example, 99.99 mol %. The ethylene unit content and saponification degree of EVOH can be determined by known methods (eg, ¹ H-NMR measurement, etc.).

EVOH is usually produced by saponifying a copolymer of ethylene and vinyl ester using an alkali catalyst or the like. As such, EVOH may contain vinyl ester units. The vinyl ester of the unit is typically vinyl acetate and may be vinyl formate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, and the like. EVOH may contain monomer units other than ethylene units, vinyl alcohol units, and vinyl ester units within a range that does not significantly impair the effects of the present invention.

Suitable good solvents for EVOH include a mixed solvent of water and alcohol, dimethylsulfoxide (DMSO), and the like. Propyl alcohol is preferable as the alcohol used in the mixed solvent. Propyl alcohol can be either n-propyl alcohol or isopropyl alcohol. Therefore, a particularly suitable good solvent is a mixed solvent of water and propyl alcohol, or DMSO.

Suitable poor solvents for EVOH include water; alcohol; cyclic esters such as γ-butyrolactone; cyclic carbonates such as propylene carbonate; cyclic sulfones such as sulfolane; Ether group-containing monools such as ether, diethylene glycol monoethyl ether and 2-ethoxyethanol, diols such as 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol and 1,6-hexanediol and the like. Among them, cyclic esters, cyclic carbonates, cyclic sulfones, or ether group-containing monools are preferable, and γ-butyrolactone, propylene carbonate, sulfolane, or ether group-containing monools are more preferable, γ-butyrolactone, or Sulfolane is more preferred. The solubility parameter (Hildebrand SP value) δ of the poor solvent is preferably greater than the solubility parameter δ of EVOH by 1.6 MPa ^1/2 or more.

In EVOH, water and alcohol are poor solvents for EVOH, but a mixed solvent of water and alcohol (especially propyl alcohol) is a good solvent. Here, the mixed solvent of water and alcohol can be regarded as a mixed solvent of water and alcohol, which is a good solvent in which water is reduced, and water, which is a poor solvent with a higher boiling point. A mixed solvent of water and alcohol can be used alone to prepare a solution of EVOH. Therefore, in the present invention, when a solvent obtained by mixing two or more poor solvents is a good solvent for a specific water-insoluble polymer, the good solvent for the water-insoluble polymer and the non-water-insoluble polymer for solution preparation As the mixed solvent containing the poor solvent for the water-soluble polymer, a mixed solvent of two or more of these poor solvents can be used alone.

2. When the Water-Insoluble Polymer is Cellulose Acetate Suitable good solvents for cellulose acetate include nitrogen-containing polar solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone (especially nitrogen-containing non-polar solvents). protic polar solvents); esters such as methyl formate and methyl acetate; ketones such as acetone and cyclohexanone; cyclic ethers such as tetrahydrofuran, dioxane and dioxolane; glycol derivatives such as methyl glycol and methyl glycol acetate; , tetrachloroethane and other halogenated hydrocarbons; cyclic carbonates such as propylene carbonate; sulfur-containing polar solvents such as DMSO (especially sulfur-containing aprotic polar solvents); Among them, sulfur-containing aprotic polar solvents are preferred, and DMSO is more preferred.

Suitable poor solvents for cellulose acetate include water; alcohols such as 1-hexanol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol and 1,6-hexanediol. . As alcohols, monohydric or dihydric alcohols having 4 to 6 carbon atoms are preferred.

3. When the water-insoluble polymer is polyvinylidene fluoride Suitable good solvents for polyvinylidene fluoride include nitrogen-containing polar solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone (especially nitrogen aprotic polar solvents); sulfur-containing polar solvents such as DMSO (particularly sulfur-containing aprotic polar solvents); Among them, nitrogen-containing aprotic polar solvents are preferred, and N,N-dimethylformamide is more preferred.

Suitable poor solvents for polyvinylidene fluoride include water; alcohols such as 1-hexanol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, and glycerin ; Cyclic ethers such as tetrahydrofuran, dioxane, dioxolane, and the like. Among them, alcohols are preferred, and dihydric or trihydric alcohols having 3 to 6 carbon atoms are more preferred.

4. When the Water-Insoluble Polymer is a Vinylidene Fluoride-Hexafluoropropylene Copolymer The vinylidene fluoride-hexafluoropropylene copolymer (P(VDF-HFP)) contains vinylidene fluoride units and hexafluoropropylene units as monomer units. It is a copolymer containing propylene units. The copolymerization ratio of these units is not particularly limited, and may be appropriately determined according to the properties of the separator. The vinylidene fluoride-hexafluoropropylene copolymer can be obtained by synthesizing according to a known method, and is commercially available (eg, Kynar FLEX 2850-00, 2800-00, 2800-20, 2750-01, manufactured by Arkema). 2500-20, 3120-50, 2851-00, 2801-00, 2821-00, 2751-00, 2501-00, etc.).

Preferred good solvents for P(VDF-HFP) include ketones such as acetone and methyl ethyl ketone; cyclic ethers such as tetrahydrofuran; nitrogen-containing polar solvents (especially nitrogen-containing aprotic polar solvents); sulfur-containing polar solvents such as DMSO (especially sulfur-containing aprotic polar solvents); As a good solvent, acetone, methyl ethyl ketone, or tetrahydrofuran is preferable, and acetone or methyl ethyl ketone is more preferable, since it can be easily removed by vaporization.

Suitable poor solvents for P(VDF-HFP) include water; 1-hexanol, 1,2-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, alcohols such as 6-hexanediol and glycerin; As the poor solvent, water or dihydric or trihydric alcohols having 3 to 6 carbon atoms are preferable from the viewpoints of low environmental load, availability, and ease of handling.

The amounts of the water-insoluble polymer, good solvent, and poor solvent to be used may be appropriately selected according to the types of these used. The amount of the water-insoluble polymer mixed is preferably 1 part by mass or more, more preferably 5 parts by mass or more, and still more preferably 10 parts by mass or more with respect to 100 parts by mass of the good solvent. The amount of the water-insoluble polymer mixed is preferably 40 parts by mass or less, more preferably 35 parts by mass or less, and even more preferably 30 parts by mass or less with respect to 100 parts by mass of the good solvent. The amount of the poor solvent mixed is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and still more preferably 30 parts by mass or more with respect to 100 parts by mass of the good solvent. The amount of the poor solvent mixed is preferably 400 parts by mass or less, more preferably 200 parts by mass or less, and even more preferably 100 parts by mass or less with respect to 100 parts by mass of the good solvent. By changing these amounts, it is possible to control the pore state (eg, porosity, pore diameter, etc.) of the resulting porous body.

The water-insoluble polymer solution may further contain components other than the water-insoluble polymer and the mixed solvent within a range that does not significantly impair the effects of the present invention.

There is no particular limitation on the method for preparing the solution of the water-insoluble polymer. The water-insoluble polymer may be dissolved in a good solvent, and the poor solvent may be added and mixed uniformly. A water-insoluble polymer may be dissolved. A known stirring device, mixing device, or the like can be used to prepare the solution. When preparing the solution of the water-insoluble polymer, ultrasonic irradiation, heating, etc. may be performed. The heating temperature is, for example, 40° C. or higher and 100° C. or lower. After preparing the solution of the water-insoluble polymer by heating, it may be cooled to the extent that the good solvent and the poor solvent are not separated. Moreover, this cooling is preferably carried out within a range in which the water-insoluble polymer does not precipitate. This is because the precipitated water-insoluble polymer can become an impurity.

Next, the drying process will be explained. In the drying step, the water-insoluble polymer solution prepared above is dried to remove the mixed solvent. The solution is then dried using superheated steam. In the drying process, a porous skeleton of water-insoluble polymer is formed. In the drying step, pores are formed by the operation of removing the mixed solvent, specifically by vaporization of the poor solvent, to obtain a porous resin body.

Typically, for example, pores are formed by phase separation of a water-insoluble polymer and a mixed solvent in which the poor solvent is concentrated. Specifically, since the poor solvent has a higher boiling point than the good solvent, the good solvent preferentially evaporates over the poor solvent in this step. As the good solvent decreases, the concentration of the poor solvent in the mixed solvent increases. Since the solubility of the water-insoluble polymer in the poor solvent is lower than the solubility in the good solvent, phase separation occurs between the water-insoluble polymer and the mixed solvent with a high concentration of the poor solvent, resulting in the formation of the water-insoluble polymer. A porous skeleton is formed. This phase separation may be a spinodal decomposition. Ultimately, the good solvent is removed to precipitate a water-insoluble polymer, and the high boiling point poor solvent is removed by vaporization to form voids. Thus, a water-insoluble polymer porous body is produced. In order to cause phase separation between the water-insoluble polymer and the mixed solvent with a high concentration of the poor solvent, the type and amount of the good solvent and the type and amount of the poor solvent should be appropriately selected.

Here, when the solution of the water-insoluble polymer is dried by heating or under reduced pressure, the surface of the solution of the water-insoluble polymer exposed to the atmosphere becomes the dry interface. At the surface of the solution and its vicinity (that is, the surface layer), the vaporization rate of the mixed solvent is higher than that inside the solution, which causes a compositional deviation between the surface layer and the inside of the solution. As a result, the surface layer of the solution does not become porous, and a skin layer is formed on the surface layer of the resulting porous resin body.

In contrast, in the present invention, drying is performed with superheated steam. Drying thus involves contacting superheated steam with a solution of a water-insoluble polymer. Therefore, drying is carried out in the presence of superheated steam, especially in a superheated steam atmosphere. Drying with superheated steam can suppress the formation of a skin layer on the surface layer of the porous resin body. The reason is considered as follows.

Superheated steam is steam obtained by heating saturated steam to 100° C. or higher. As shown in FIG. 1, superheated steam has much higher enthalpy than hot air, and the heat transfer method is a combined heat transfer of convection, radiation and condensation. Therefore, superheated steam enables rapid heating compared to heating methods such as hot air.

When the water-insoluble polymer solution is placed in the presence of superheated steam, condensation of the superheated steam occurs on the surface of the water-insoluble polymer solution, and a water layer is formed on the surface of the water-insoluble polymer solution. It is formed. By heat transfer from this water layer, the solvent contained in the water-insoluble polymer solution and the water in the water layer are vaporized, and the water-insoluble polymer solution is dried. Here, since water is a poor solvent for the water-insoluble polymer, water causes phase separation in the surface layer of the solution of the water-insoluble polymer. A hole is formed. Therefore, by drying with superheated steam, the surface layer of the water-insoluble polymer solution can be positively made porous, and the resulting porous resin body forms a skin layer on the surface layer. can be suppressed.

Drying of the water-insoluble polymer solution with superheated steam is accomplished, for example, by introducing superheated steam generated by a known method into a drying oven, drying chamber, or the like, and placing the water-insoluble polymer solution in the drying oven, drying chamber, or the like. It can be done by Since the superheated steam is steam of 100° C. or higher, the drying temperature is 100° C. or higher, preferably 140° C. or higher, more preferably 150° C. or higher and 200° C. or lower. A specific example of a method for carrying out the drying step will be described below.

A drying furnace capable of introducing superheated steam is prepared. FIG. 2 shows a configuration example of the drying oven. In the example shown in FIG. 2 , a heat exchanger 40 as heating means is connected to the drying furnace 10 via a superheated steam introduction pipe 20 . The drying oven 10 may be of a batch type or a continuous type equipped with a belt conveyor or the like. The superheated steam introduction pipe 20 has a first valve 30 . The heat exchanger 40 is electrically connected to the control board 50 . The heat exchanger 40 internally includes a tube (not shown) serving as a heat medium flow path. The heat exchanger 40 is connected via a steam introduction pipe 60 to a boiler 80 as steam generating means. The steam introduction pipe 60 has a second valve 70 .

Steam is generated in the boiler 80 with the first valve 30 and the second valve 70 closed. The second valve 70 is opened to introduce steam into the heat exchanger 40 through the steam inlet pipe 60 . A heat medium is passed through the tubes in the heat exchanger 40 to heat steam through the tubes. At this time, the temperature and flow velocity of the heat medium are controlled by the control panel 50 . The temperature of the heat medium is appropriately selected from temperatures exceeding 100° C. according to the temperature inside the drying furnace 10 . This heating changes the steam into superheated steam. In addition, superheated steam can also be produced|generated using a well-known superheated steam generator.

The first valve 30 is opened to introduce superheated steam into the drying furnace 10 through the superheated steam introduction pipe 20 . At this time, the inside of the drying oven 10 is heated to 100° C. or higher so that the superheated steam does not condense inside the drying oven 10 . The temperature in the drying furnace is preferably 140°C or higher, more preferably 150°C or higher and 200°C or lower. In the drying process, when the mixed solvent evaporates, heat is removed from the solution of the water-insoluble polymer and the solution is cooled. lower than the temperature of Therefore, the temperature in the drying oven may be higher than the melting point of the water-insoluble polymer.

A water-insoluble polymer solution is placed in a drying oven 10 into which superheated steam is introduced. The superheated steam and the solution of the water-insoluble polymer are brought into contact with each other, and the mixed solvent in the solution is vaporized by the heat of the superheated steam, and drying is performed. It is preferable to continue to introduce superheated steam into the drying oven 10 during drying.

When obtaining a porous body with a desired shape, a method of putting a solution of a water-insoluble polymer into a mold having a shape corresponding to the desired shape and drying it with superheated steam can be preferably used. When obtaining a film-like porous body, a method of coating a solution of a water-insoluble polymer in the form of a thin film on the surface of a substrate and drying it with superheated steam can be preferably used.

In the present invention, it is preferable to obtain a film-like porous body because of its many useful uses. Therefore, the production method according to the present invention includes a step of applying a solution of a water-insoluble polymer prepared on the surface of a substrate in a thin film form (hereinafter referred to as Also referred to as a "coating step").

The coating step for obtaining a film-like resin porous body will be described in detail. The substrate used is not particularly limited as long as it can function as a substrate. The substrate may be used after being finally peeled off from the porous body, or may be used without being peeled off. The shape of the substrate is not particularly limited, and one having a flat surface is preferable. Examples of shapes include sheet-like, film-like, foil-like, and plate-like. Examples of the constituent material of the base material include resin, glass, and metal.

Examples of the above resins include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethylene (PE), polypropylene (PP), polystyrene, polyvinyl chloride, poly(meth)acrylate, polycarbonate, polyimide, polyamide, and polyamideimide. etc.

Examples of the metals include aluminum, copper, nickel, stainless steel, and the like. In addition, a base material using a plurality of materials such as fiber-reinforced resin such as glass-fiber-reinforced epoxy resin can be used.

Moreover, the base material may have a multilayer structure. For example, the substrate may have a release layer containing fluororesin. For example, the substrate may be paper or the like having a resin layer.

When the substrate is used without peeling, it may have a role as a functional layer of the resulting porous resin body. For example, the base material may have functions such as a reinforcing material and a supporting material. The substrate may also be an electrode of a secondary battery (especially an active material layer of an electrode of a secondary battery). At this time, the method for manufacturing the resin porous body can be used as the method for manufacturing the electrode-integrated separator of the secondary battery.

The method of applying the water-insoluble polymer solution is not particularly limited, and may be appropriately selected according to the type of substrate. Examples of coating methods include die coating, gravure coating, roll coating, spin coating, dip coating, bar coating, blade coating, spray coating and casting. The thickness of the coating is not particularly limited, and may be appropriately set according to the application of the porous body.

A membrane-like porous resin material (that is, a porous resin membrane) is obtained by subjecting the solution of the water-insoluble polymer coated on the substrate obtained as described above to a drying process. can be done.

As described above, porous resin bodies having various shapes including film shapes can be obtained. Since the formation of a skin layer is suppressed, the porous resin body has a three-dimensional network-like porous structure in which pores are communicated from one principal surface to the opposite principal surface. According to the production method of the present invention, the average pore size is, for example, 0.5 μm or more (especially 0.9 μm or more, further 1.4 μm or more) and 5 μm or less (especially 4.2 μm or less, further 3.8 μm or less). You can get quality. The average pore size can be obtained by taking cross-sectional electron micrographs of the porous body and calculating the average value of 100 or more pore sizes. When the cross section of the pore is non-spherical, the pore diameter may be the average of the maximum diameter and the minimum diameter of the pore. Further, according to the production method of the present invention, the porosity is, for example, 15% or more (especially 42% or more, further 51.5% or more, further 61.5% or more) and less than 80% (especially less than 75%) ) can be obtained. In addition, the porosity can be calculated using a true density and an apparent density according to a known method.

According to the present invention, there is no need to perform the operation of cooling to precipitate a molded article and the operation of replacing the solvent, and the process of preparing a solution of a water-insoluble polymer and removing the good solvent and the poor solvent by drying. , a resin porous body can be produced. That is, according to the present invention, a porous resin body can be produced with a small number of steps. Further, in the present invention, the formation of a skin layer on the surface layer of the porous resin body is suppressed. Therefore, the resin porous body can be used in a wide range of applications.

Examples of applications of the porous resin material include packaging materials, building materials, sound absorbing materials, cleaning products, cosmetic products, separation membranes, adsorbents, purification carriers, catalyst carriers, culture carriers, and the like. In addition, the resin porous body can be used as a separator for a secondary battery, utilizing the fact that the electrolyte can permeate through the porous resin because it does not have a skin layer. When the porous resin body is applied to the separator, the separator can be formed directly on the active material layer, which is advantageous in terms of separator production.

Therefore, the above-described production method includes a step of preparing a solution in which the water-insoluble polymer is dissolved in a mixed solvent containing a good solvent for the water-insoluble polymer and a poor solvent for the water-insoluble polymer; The step of coating the prepared solution on the active material layer of the electrode, and the step of drying the coated solution to remove the mixed solvent, wherein the boiling point of the poor solvent is It has a higher boiling point than the solvent, and can be applied as a method for manufacturing an electrode-integrated separator for a secondary battery in which the applied solution is dried using superheated steam.

When the electrode is a positive electrode, the active material layer (ie, positive electrode active material layer) may contain a positive electrode active material. Examples of positive electrode active materials include lithium transition metal oxides (eg, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNiO ₂ , LiCoO ₂ , LiFeO ₂ , LiMn ₂ O ₄ , LiNi _0.5 Mn _{1 .5O4 ,} etc.), lithium transition metal phosphate compounds (eg, _LiFePO4, etc.), and the like. The positive electrode active material layer may contain components other than the active material, such as a conductive material, a binder, and lithium phosphate. Carbon black such as acetylene black (AB) and other carbon materials (eg, graphite) can be suitably used as the conductive material. As the binder, for example, polyvinylidene fluoride (PVDF) or the like can be used.

When the electrode is the negative electrode, the active material layer (that is, the negative electrode active material layer) may contain the negative electrode active material. Examples of negative electrode active materials include carbon materials such as graphite, hard carbon, and soft carbon. The negative electrode active material layer may contain components other than the active material, such as binders and thickeners. As the binder, for example, styrene-butadiene rubber (SBR) or the like can be used. As a thickening agent, for example, carboxymethyl cellulose (CMC) or the like can be used.

An active material layer is typically formed on the current collector. Examples of current collectors include aluminum foil and copper foil.

The operation of each step is as described above. This method for producing an electrode-integrated separator for a secondary battery is extremely excellent in that the electrode-integrated separator for a secondary battery can be manufactured in a small number of steps.

The separator-integrated electrode manufactured as described above can be used in various secondary batteries according to known methods. The secondary battery is preferably a lithium secondary battery, and the lithium secondary battery can be used as a portable power source for personal computers, mobile terminals, etc., electric vehicles (EV), hybrid vehicles (HV), plug-in hybrid vehicles (PHV). ), etc., can be suitably used as a power source for driving a vehicle.

EXAMPLES Examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the examples.

Example 1
2.1 parts by mass of cellulose acetate (manufactured by Aldrich, average molecular weight: 50,000) was weighed into a sample bottle. 10 parts by mass of acetone as a good solvent was added to this sample bottle. The sample bottle was heated to 40° C.-50° C. to completely dissolve the cellulose acetate in the acetone. After that, 1.5 parts by mass of water as a poor solvent was added to the sample bottle and stirred. Thus, a cellulose acetate solution was obtained in which the solvent was a mixed solvent of acetone/water.

A cellulose acetate solution was applied by casting onto an aluminum foil as a substrate. At this time, the coating thickness was 200 μm.

A belt-conveyor type drying furnace was prepared in which a heat exchanger was connected upstream and a boiler was further connected upstream. Steam was generated in a boiler, sent to a heat exchanger, heated, and changed to superheated steam. The temperature inside the drying furnace was set to 150°C, this superheated steam was fed into the drying furnace at a flow rate of 100 kg/hr, and the temperature inside the drying furnace was kept on standby until the temperature stabilized at 150°C. After that, the aluminum foil coated with the cellulose acetate solution was placed in a drying oven and dried for 60 seconds to remove the mixed solvent of acetone/water. Thus, a porous film of cellulose acetate was obtained on the aluminum foil.

Example 2
A porous membrane of cellulose acetate was produced in the same manner as in Example 1, except that the temperature in the drying oven was changed to 200°C.

Comparative example 1
The cellulose acetate solution prepared in Example 1 was applied by casting onto an aluminum foil as a substrate. At this time, the coating thickness was 200 μm. The aluminum foil coated with the cellulose acetate solution was placed in a hot air dryer set at 30° C. and dried for 60 seconds to remove the mixed solvent of acetone/water. Thus, a porous film of cellulose acetate was obtained on the aluminum foil.

Comparative example 2
The cellulose acetate solution prepared in Example 1 was applied by casting onto an aluminum foil as a substrate. At this time, the coating thickness was 200 μm. The aluminum foil coated with the cellulose acetate solution was placed in a hot air dryer set at 60° C. and dried for 60 seconds to remove the mixed solvent of acetone/water. Thus, a porous film of cellulose acetate was obtained on the aluminum foil.

Comparative example 3
The cellulose acetate solution prepared in Example 1 was applied by casting onto an aluminum foil as a substrate. At this time, the coating thickness was 200 μm. The aluminum foil coated with the cellulose acetate solution was placed on a hot plate whose surface temperature was set to 50° C. and dried for 60 seconds to remove the mixed solvent of acetone/water. Thus, a porous film of cellulose acetate was obtained on the aluminum foil.

Example 3
Vinylidene fluoride-hexafluoropropylene copolymer (“Kynar-FLEX 2821-00” manufactured by Arkema, grade: powder type, hereinafter referred to as “P (VDF-HFP)”) 1.0 part by mass was weighed into a sample bottle. bottom. 3.2 parts by mass of methyl ethyl ketone (MEK) as a good solvent was added to this sample bottle. The sample bottle was heated to 40-50°C to completely dissolve P(VDF-HFP) in MEK. After that, 0.4 parts by mass of 1,2-propanediol as a poor solvent was added to the sample bottle and stirred. In this way, a P(VDF-HFP) solution was obtained in which the solvent was a mixed solvent of MEK/propanediol.

A P(VDF-HFP) solution was applied by casting onto an aluminum foil as a substrate. At this time, the coating thickness was 200 μm.

A belt-conveyor type drying furnace was prepared in which a heat exchanger was connected upstream and a boiler was further connected upstream. Steam was generated in a boiler, sent to a heat exchanger, heated, and changed to superheated steam. The temperature inside the drying furnace was set to 170°C, this superheated steam was fed into the drying furnace at a flow rate of 100 kg/hr, and the temperature inside the drying furnace was kept on standby until the temperature stabilized at 170°C. Thereafter, the aluminum foil coated with the P(VDF-HFP) solution was introduced into a drying oven and dried for 60 seconds to remove the mixed solvent of MEK/propanediol. Thus, a porous film of P(VDF-HFP) was obtained on the aluminum foil.

Example 4
A porous film of P(VDF-HFP) was obtained on an aluminum foil in the same manner as in Example 3, except that the temperature in the drying oven was set to 200°C.

Comparative example 4
The P(VDF-HFP) solution prepared in Example 3 was applied by casting onto an aluminum foil as a substrate. At this time, the coating thickness was 200 μm. The aluminum foil coated with the P(VDF-HFP) solution was introduced into a hot air dryer set at 100° C. and dried for 60 seconds to remove the MEK/propanediol mixed solvent. Thus, a porous film of P(VDF-HFP) was obtained on the aluminum foil.

Comparative example 5
The P(VDF-HFP) solution prepared in Example 3 was applied by casting onto an aluminum foil as a substrate. At this time, the coating thickness was 200 μm. The aluminum foil coated with the P(VDF-HFP) solution was placed on a hot plate whose surface temperature was set to 80° C. and dried for 60 seconds to remove the mixed solvent of MEK/propanediol. Thus, a porous film of P(VDF-HFP) was obtained on the aluminum foil.

[Evaluation of liquid penetration]
Ethanol was dropped on the surface of the porous membrane obtained in each example and each comparative example, and whether or not the ethanol permeated to the back surface of the porous membrane was visually evaluated. Table 1 shows the results. When ethanol permeates to the back surface of the porous membrane, it can be determined that there is no skin layer and the entire membrane is made porous. On the other hand, when ethanol does not permeate, it can be determined that a skin layer is formed on the surface layer of the porous membrane.

[Evaluation by SEM observation]
The surfaces of the porous membranes obtained in Comparative Example 1 and Examples 1 and 3 were observed with a scanning electron microscope (SEM). SEM photographs of the surfaces of the porous membranes obtained in Comparative Example 1 and Examples 1 and 3 are shown in FIGS. 3 to 5, respectively.

As the results in Table 1 show, in Comparative Example 1 in which hot air drying was performed, ethanol did not permeate the back surface of the porous membrane. Furthermore, as shown in the SEM image (FIG. 3), no pores were observed on the surface of the porous membrane obtained in Comparative Example 1. From this, it can be seen that in Comparative Example 1, a skin layer was formed on the surface of the porous membrane. In addition, in Comparative Example 2 in which the temperature of the hot air was increased, and in Comparative Example 3 in which the heating method was changed to a hot plate, ethanol did not permeate to the back surface of the porous membrane and a skin layer was formed.

On the other hand, in Examples 1 and 2 in which drying was performed using superheated steam, ethanol penetrated to the back surface of the porous membrane. Furthermore, as shown in the SEM image (Fig. 4), it was confirmed that many pores were formed on the surfaces of the porous membranes obtained in Examples 1 and 2. From this, it can be seen that the porous membranes obtained in Examples 1 and 2 were made porous without forming a skin layer. In addition, between Example 1 and Example 2, there was no difference in the porous structure of the obtained porous films.

In addition, from the results of Examples 3 and 4 and Comparative Examples 4 and 5, as well as from FIG. 5, even when the type of resin is changed, the skin layer is not formed by drying with superheated steam. It turns out that it was made porous. From this, it can be seen that the effect of suppressing the formation of a skin layer by drying with superheated steam is exerted on resins (that is, water-insoluble polymers) for which water is a poor solvent.

In the above examples, the steps required for producing the porous resin material are the preparation of the water-insoluble polymer solution and the removal of the mixed solvent by drying. Therefore, according to the present invention, it is possible to produce a porous resin body in which the formation of a skin layer is suppressed using a water-insoluble polymer with a small number of steps.

10 drying furnace 20 superheated steam introduction pipe 30 first valve 40 heat exchanger 50 control panel 60 steam introduction pipe 70 second valve 80 boiler

Claims (5)

preparing a solution in which the water-insoluble polymer is dissolved in a mixed solvent containing a good solvent for the water-insoluble polymer and a poor solvent for the water-insoluble polymer;
drying the solution to remove the mixed solvent;
encompasses
The boiling point of the poor solvent is higher than the boiling point of the good solvent,
drying the solution with superheated steam;
A method for producing a resin porous body. After the step of preparing the solution and before the step of drying the solution, the step of coating the prepared solution of the water-insoluble polymer on the surface of the substrate in a thin film form, further comprising: The manufacturing method according to claim 1. 3. The manufacturing method according to claim 2, wherein the substrate is an electrode of a secondary battery. The production method according to any one of claims 1 to 3, wherein the water-insoluble polymer is an ethylene-vinyl alcohol copolymer or a vinylidene fluoride-hexafluoropropylene copolymer. The production method according to any one of claims 1 to 4, wherein the drying of the solution is performed using superheated steam at a temperature of 140°C or higher.

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